The test uses a so-called adaptive procedure: after a correct response we make it harder, after an incorrect one we make it easier. The advantage of such a procedure is that it can produce an accurate and reliable estimate of your localisation skills very quickly. The downside of that is that you will be close to your perceptual threshold for most of the test duration, which means that you will have to do a lot of guessing. On average about 75% of the presentations will have such a small angle between the two sounds that you will not be sure whether you gave the right answer or not. Do not let this deter you and keep on giving your best guesses.
When you do the test you will find that the there is a timbre associated with the sounds that you hear. This timbre can vary somewhat from sound to sound. Unfortunately this is not a reliable cue to do the test with. Instead, keep looking forward and concentrate on the positions from which the sounds appear to come. Do they move from left to right or in the opposite direction?
Remember that each presentation has two noise burst, that together make a single direction.